This application claims the benefit of Korean Patent Application No. 2001-5942 filed on Feb. 7, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a disc drive, and more particularly, to an automatic power control apparatus reducing the time necessary for stabilizing an automatic power control circuit at the initial stage of automatic power control of a disc drive.
2. Description of the Related Art
Disc drives such as CD drives, DVD drives, CD-ROM drives and DVD-ROM drives write and read data to and from a disc by use of write signals to the disc or read signals from the disc using light. Disc drives write data to a disc by radiating light on the disc from the laser diode and read data from the disc by applying an optical signal to the disc from the laser diode with current lower than a writing power, converting light reflected from the disc into an electrical signal using a light receiving diode (i.e., a photodetector), and processing the signal. Such disc drives essentially need an automatic power control (APC) circuit to automatically control driving current of the laser diode to control the power of an optical signal output from the laser diode to be constant in a write or read mode.
As shown in FIG. 1, a conventional APC apparatus includes an operational (OP) amplifier A1, resistors R1 and R2, and a capacitor C1. A reference voltage Ref is applied to the non-inverted input terminal of the OP amplifier A1 as shown in FIG. 2A, and a sampling and holding (S/H) voltage of a signal that monitors writing power is applied to the inverted input terminal of the OP amplifier A1, thus providing a beginning signal shown in FIG. 2B.
Once a command for a write mode is input to a disc drive, an output voltage gradually increases depending on a time constant which is determined by the resistor R1 and the capacitor C1 starting from a point when APC in the write mode begins, as shown in FIG. 2C.
An APC stabilizing time (i.e., to in FIG. 2C) considerably influences the quality of writing. As the APC stabilizing time becomes shorter, an amount of lost data can be reduced. Particularly, as the speed factor of a disc drive gradually increases to 8xc3x97 and then to, 12xc3x97, the APC stabilizing time at an initial stage of a write mode increasingly influences the writing quality.
Accordingly, since a conventional APC apparatus needs some time starting from a point when APC begins until laser power is stabilized, an error occurs before the power of a laser diode reaches a predetermined level due to a deficiency of the output power of the laser diode in a write mode.
Accordingly, it is an object of the present invention to provide an automatic power control apparatus reducing a stabilizing time at an initial stage of automatic power control of a laser diode in a disc drive by initially applying an additional predetermined voltage to an automatic power control circuit.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing objects of the present invention are achieved by providing an automatic power control apparatus of a disc drive, including a controller generating an automatic power control reference voltage signal and a stabilizing compensation voltage signal which are suitable for a selected mode; an amplifier receiving the automatic power control reference voltage signal from the controller, and a signal which is obtained by sampling a writing section of a monitor signal that estimates the level of the output power of a laser diode, through its two input terminals, respectively, and amplifying the voltage difference between the two signals at its input terminals with predetermined gain; and an adder summing the output of the amplifier and the stabilizing compensation voltage signal and outputting the result of the summation to a laser diode driving circuit.